Add assert_threads_result helper and threads test

CONTRIBUTING.md

@@ -372,6 +372,23 @@ An variable entry looks like this: `{ name: "bar", value: "nil", type: "NilClass
 
 Please note that both `value` and `type` need to be strings.
 
+- assert_threads_result(expected)
+
+Passes if both conditions are true:
+
+1. The number of expected patterns matches the number of threads.
+2. Every pattern matches a thread name. Notice that the order of threads info is not guaranteed.
+
+Example:
+
+```
+assert_threads_result(
+ [
+ /\.rb:\d:in `<main>'/,
+ /\.rb:\d:in `block in foo'/
+ ]
+)
+```
 
 ## To Update README
 

test/protocol/threads_test.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require_relative '../support/test_case'
+
+module DEBUGGER__
+ class ThreadsTest < TestCase
+ PROGRAM = <<~RUBY
+ 1| def foo
+ 2| Thread.new { sleep 30 }
+ 3| end
+ 4|
+ 5| foo
+ 6| sleep 0.1 # make sure the thread stops
+ 7| binding.b
+ RUBY
+
+ def test_reponse_returns_correct_threads_info
+ run_protocol_scenario PROGRAM, cdp: false do
+ req_continue
+
+ assert_threads_result(
+ [
+ /\.rb:\d:in `<main>'/,
+ /\.rb:\d:in `block in foo'/
+ ]
+ )
+
+ req_terminate_debuggee
+ end
+ end
+ end
+end
+

test/support/protocol_utils.rb

@@ -230,6 +230,29 @@ def assert_locals_result expected, frame_idx: 0
  end
  end
 
+ def assert_threads_result(expected_names)
+ case ENV['RUBY_DEBUG_TEST_UI']
+ when 'vscode'
+ res = send_dap_request 'threads'
+ failure_msg = FailureMessage.new{create_protocol_message "result:\n#{JSON.pretty_generate res}."}
+
+ threads = res.dig(:body, :threads)
+
+ assert_equal expected_names.count, threads.count, failure_msg
+
+ thread_names = threads.map { |t| t[:name] }
+
+ expected_names.each do |expected|
+ thread_names.reject! do |name|
+ name.match?(expected)
+ end
+ end
+
+ failure_msg = FailureMessage.new{create_protocol_message "result:\n#{JSON.pretty_generate res}.\nExpect all thread names to be matched. Unmatched threads:"}
+ assert_equal [], thread_names, failure_msg
+ end
+ end
+
  def assert_hover_result expected, expression: nil, frame_idx: 0
  case ENV['RUBY_DEBUG_TEST_UI']
  when 'vscode'